Sealing Vacuum Leak in Welded Al Tool 1

[ArturoJones]

We have a welded aluminum tool which has developed a vacuum leak(s) at the weld. The tool sees 300ºF during the cure cycle.
The two options I have contemplated to fix this are a) to grind out, re-weld and re-finish the tool surface or b)seal from the backside with an epoxy sealant. I don't like the first option because I am concerned about distorting the tool but I'm skeptical about the chances of success with the second method.

The insight of anyone who has had experience with this problem would be appreciated. I've done the google search for tool sealants, but any specific products and techniques which have been successful for people would be helpful. Thanks.

 

[Compositepro]

Use silicone to seal the backside while pulling vacuum on your tool. If you use a sensitive gage like a mercury manometer you should be able to see when you have sealed the leak. Most epoxies are too stiff and will crack after thermocycling because of the high thermal expansion difference the epoxy and aluminum. Silicone will not crack.
A heat cured silicone would be best but RTV will work in most cases. Just let it cure un-bagged for at least a day after sealing.